Such a switching mat, also referred to as switching mat or keyboard mat, is the central component in many operating members, particularly those with a key switching functionality. It determines the feel, i.e. the tactile impression, but also the electrical behavior via the integrated contact pill. Such switching mats, which are disposed above a circuit board, also referred to as printed circuit board, are usually made from silicone rubber and, due to the combination of tactile feel or return action and electrical switching function, provide for a high integration density, but also, due to the two-dimensional configuration, for protection in order to prevent dust, dirt and liquid from entering the contacting portion of the operation member. A frustoconical or bell-shaped dome, which transitions into a cylinder in, for example, the central axis, is usually formed from the basic material silicone rubber. A unilaterally open cavity placed on the circuit board is defined underneath the dome. The outer end of the cylinder constitutes the point of application for an actuating part. The inner end of the cylinder situated in the cavity has a contact pill made of electrically conductive material and constitutes the electrical contact member. The contact pill usually cooperates with an open contacting portion, which is disposed underneath the dome on the circuit board and which is bridged by the contact pill. Mostly, several key switches are realized at once in a single switching mat; however, there are also individual operating members based on a switching mat.
The tactile feel of the operating member can be adapted over a wide range via the shape of the dome or the webs and the material properties of the basic material. A tactile feedback during the actuation of an operating member increases operational reliability because it permits a user to immediately recognize whether a function has been triggered. In contrast to an acoustic feedback, a tactile feedback is advantageous in that it can be easily perceived also in an environment with ambient noise, particularly in an automobile.
Though it is possible to determine the electrical properties of the operating member through the selection of the contact pill, however, due to the fact that the contact pill is disposed in the cavity defined by the associated tactile-feel dome, its geometrical design, however, is limited as regards its thickness and size by the dimensions of the respective cavity. In addition, the contact pill is subject to mechanical wear which, as a rule, affects the switching function. Due to the limitation of the cavity as regards space, this cannot be counteracted by a corresponding design of the contact pill, for example.
Therefore, there is a demand for a design of the operating member in which this limitation is removed, if possible, and which on the whole results in a more reliable, in particular more temperature-resistant, operating member.